Growth, characterization and transport properties of Pb x Zn1−x S mixed crystals

Abstract

The polycrystalline Pb x Zn1−x S semiconductor powder with (0 ≤ x ≤ 0·5) has been prepared by controlled co-precipitation method from an alkaline medium using thiourea as a sulphide ion source. Pellets are made with these powders applying 10 ton/sq.cm. pressure and sintered at 800°C for 2 h in nitrogen atmosphere. X-ray studies of these samples have indicated that the compounds are polycrystalline in nature with mixed hexagonal and cubic structure of ZnS and cubic structure of PbS. Lattice parameters (a and c) of all the compounds are determined from the X-ray data and are found to decrease nonlinearly with increase in Pb concentration (x). It is also observed that the grain size of the crystallites increases in samples with x = 0−0·5. Scanning electron micrographs have shown that both cubic and hexagonal crystallites are present in the mixed crystals. The electrical conductivity in Pb x Zn1−x S is found to decrease with increase in composition (x = 0−0·5), whereas it increases at all temperatures in all samples. Mobility of charge carrier concentration is found to increase with increasing temperature. The increase in carrier mobility in Pb x Zn1−x S samples may be due to reduced grain boundary potential. In Pb x Zn1−x S samples with x = 0−0.3, the sum of the activation energy due to charge carriers and grain boundary potential is equal to the activation energy due to conductivity.